This project is a home-built bike light using Malibu sidewalk flood lights you can buy at Home Depot or most hardware stores. The project is inexpensive to build and easy to do. My first Malibu light has held up well in some really challenging conditions like several bike falls, dust storms and rain so I feel confident about it's general utility.
They put out a good amount of light compared to LED bike lights. I have a LED light on my helmet for extra backup which is an excellent idea. The bike-mounted light points in your direction of travel and is very visible to vehicles and other travelers. The LED helmet light is a backup and points in the direction you are looking at, like your bike lock at night or a car in your vicinity.
More light is better for anyone traveling at night.
Step 1: Get the Parts
The light is a standard Malibu light available in most places that sell lighting. It's used for lighting sidewalks.
This unit is a slightly higher end model at $15 compared to the $9 units I've used previously. The advantage of this unit is that the cheapest Malibu has an extended light barrel on the end of the light which is a stylistic add-on I think. The barrel has an extended lip on top. If you hang the light upside down on your bars, the barrel can be rotated but the lip won't be at the top of the light. Annoying.
Also, the light below is using an MR16 bulb and seems to put out more light at the same wattage than the lower end Malibu. Plus the body has ribs.
The light also has an adjusting screw that you can loosen then rotate the light vertically. That's a big help when you're dialing it in.
So, one Malibu light.
Some lamp cord. Long enough to go to wherever you plan to put your battery plus some extra slack.
I'm using a lighted switch below. You can also use a lamp cord switch for $1. That's cheaper but has the drawback that there's no visible signal to you that your light is on. You'll find out why that's important the first time you have your light on in somewhat bright conditions and forget to turn it off, draining your battery.
The connectors are called Powerpoles. They are genderless and work pretty well. I don't like the look particularly when they are exposed but that's what I'm using until I find another way.
Some folks use stereo plugs.
The switch is mounted on a conduit hangar. It's basically a metal u-shape that has a oval in the middle that fits most handlebars handily. The screw is behind the lamp cord in the picture. Very cheap and easy to use.
12V lead acid battery. I use these because they are inexpensive with good capacity.
The 7.5 amp hour batteries have thinner profiles than the 4.5ah or 12ah ones. I use them because they are a nice middle range between the 4.5ah (easy to mount with lower capacity) and the 12ah (big, heavy bricks).
I fuse my batteries because there's nothing like getting electric current through delicate body parts to ruin your whole day, not to mention catching on fire or getting a nasty burn.
So, one blade fuse available just about anywhere. I use a 10amp fuse. The fuse should be 1.5x greater than the amps in the circuit. so I guess it should be 20watts=12Volts x Amps = 1.6Amps in the circuit times 1.5 = 2.5 Amp fuse nominal.
The switch is a lighted switch for 12V circuits. i found one at an electronics store.
You'll also need a charger for your battery. I found an inexpensive one at an electronics store. The charger has to match the type of battery you are using. It's better to pay a little more for a charger than get the cheapest one you can find.
Light - $15
Switch - $3.50
Conduit hanger - .50
Lamp cord - $2
Battery (ebay) - $20 w/delivery
plus a couple of crimp on connectors for your battery posts, plus maybe some electrical tape.
Charger - $15 - $50 depending on what type you get.
Step 2: The Light
Okay, here's the light.
You can see the light has a stake at the bottom. The gray streak down the center is the front part of the cross bar that's been cut off, meaning that if you looked at the stake from end-on when you bought it, it would look like a right-angle cross.
That long stake and the cross shape isn't going to fasten too easily to a round handlebar so I cut off the end, then cut off the cross bar on front and back so the stake is a shorter piece of flat metal.
A hacksaw would probably do it. I use a zip tool.
The electrical connectors that come with it are designed to punch into a 12V line. I cut them off and put on my connectors.
It helps to put electrical tape around the seam of the barrel at the business end of the light. It fastens on well but isn't waterproof though it's designed to be outside all day. Your mileage may vary.
Step 3: The Switch
For mounting the switch to the hangar, I took a short piece of flat aluminum stock, drilled a hole in one side for the switch to mount, and a smaller hole for the conduit hangar, then put them together.
I'm using crimp-ons for the bottom electrical connections. The next step is the circuit diagram which will explain things further, however, notice that the ground from the light is spliced to the ground connection to the battery at the switch pole which also needs to go to ground.
The little light in the switch needs a ground to work correctly. The worst thing about the switches you commonly find is that the package doesn't specify the ground, positive and load with anything approaching certainty for a newbie to electronics. So ask the clerk if you aren't sure or look for a switch with better packaging.
This switch I'm happy with as it lights up fairly well.
As I mentioned earlier, you can use a lamp cord switch also. I like lighted because you get a reminder when your light is on. Plus it looks cool.
Step 4: Circuit Diagram
The big square on the left is the battery with plus and minus posts, the fuse is in the positive side of the circuit along with the switch. The switch needs one post to go to ground (connect to the negative pole). The other two connect to the battery positive circuit and the light positive circuit.
The third post on the switch is the negative pole of the switch internal light, so for it to work it has to go to ground.
If you use a lamp cord switch, the circuit is simplified as the third post on the switch is eliminated. I haven't tried a lamp cord switch as it seems a little cheesy for me in an outdoors situation but they would do the job and are inexpensive.
Step 5: The Battery
I put a couple of loops of tape around the battery posts so they can't accidentally form a ground, then I tape down the fuse to the block so it can't go anywhere. That ends up being a fairly tight and secure package.
Just as a note, when you go to charge the battery, you'll need to unfasten your connector and connect the charger. I leave the battery on my bike, unplug the powerpole pair either at the light or the battery and hook up the charger that's also got powerpoles on it to match.
You could also splice in a matching positive and negative connector that matches your existing charger connectors. Imagine the setup below except the two blue crimp-ons at the battery posts have an extra set of wires and connectors spliced in that mate with your charger. That way you could hardwire the whole setup minus the powerpoles and just plug in the charger when you need to.
Just remember: positive to positive, negative to negative. PowerPoles make that easy but you need a cheap crimping tool and a few practice runs to get them done right.
Step 6: Mounting the Light
Mounting a flat piece of metal to a round bar takes some ingenuity. I usually rummage through my box-o-bike-parts and see what might work.
On this bike I took an old bike speedometer bracket (minus the speedometer) and put the light stake into the bracket which had a convenient taper matching the stake's taper. Then I zip-tied it.
This particular setup gets no kudos for style. I said earlier that I had cut off the back part of the cross on the stake, but I can see it's still there.
If I was to redo this, I would cut off the back part of the stake cross, drill a hole in the stake and use a conduit hanger just like the switch next to it.
As a post-project critique, the setup has a bit too many hard edges. You never know when you are going to have a body part go in an unusual direction and sharp pointed corners have a way of creating painful contusions, so upon reflection, I will round off the sharp corners you see in this picture.
Step 7: Hey, It Works!
So, I included a couple of shots of the whole bike. These lights work nicely, giving you perhaps 20-30 feet of illumination in front of you bike.
The only drawback with this Malibu is that the MR16 bulb fixture inside is not designed to be on a bike, so the bulb can come loose and start to rattle around. The bulb can't go anywhere as there's a glass front but it can get loose and rattle against the body which I find annoying on a ride..
The cheaper Malibu didn't do this ever. I haven't tested this light enough to know if it's a constant problem. I may have to put a heat proof retainer inside the light if it proves to be a continuing issue. I haven't used it enough to know for sure but I had to push it into place one or twice and then it seemed stable.
The lamp cord is tied down with zip ties, and the battery lives semi-permanently in a pannier.
I prefer to bring the power to the bike, not the battery to the charger, so keep that it mind. If you mount the battery, make sure you can get it off easily or get the charger power to it.